Born from a military experiment gone wrong, the Titans were large beasts many times the size of a normal human. They boasted incredible resilience, able to regenerate from normally lethal damage. Furthermore, they had a self-sustaining metabolism that made eating unnecessary. Despite this, though, the beasts had a fixation on eating people, making them very dangerous.

Initially, the Titans were created through injecting a substance into a human, causing mutations. These experiments were performed, in secret, for decades. At first the beasts were used as weapons, deployed in areas as a form of attack. This practice proved fatal to humanity, as a virus, bore from the Titans, began to spread. As a result, the situation quickly went out of control. Normal people in residential areas were suddenly transforming into mindless Titans. The creatures spread the world over, with the world's military unable to stop them. Devouring humans as they went, the Titans ushered the world into a post-apocalyptic state.

Eventually, in Japan, huge walls were constructed to protect the population. Multiple layers were built, to safeguard in the situation one should fall. Garrisons were also established, as an added defense to help protect the barriers. The last survivors were then rushed into the walled area, leaving an abandoned wasteland beyond. Humanity lived in relative peace inside, as over a hundred years passed since the birth of the Titans. In that time, a weakness for the beasts was discovered. If the nape, the back of the neck, of a Titan was destroyed, the creature would die. Furthermore, it was realized that the Titans had relatively poor eyesight. This meant the beasts were more active when it was light. These were not seen as overly exploitable, though, and no attempts to reclaim the outside were made.

As the virus no longer seemed active, humanity became accustomed to life inside the walls. In fact, as the fear started to dissipate, new generations regarded the Titans as legends. That all changed, though, from the appearance of a new, larger Titan outside the wall. This 120 meter creature was tall enough to see over the giant barriers. The creature destroyed part of the outer wall in the Monzen District, creating a large hole. Quickly after the destruction, the monster vanished in a cloud of steam.

The nightmare had only just begun, though. From the hole, Titans began to emerge. The stationed garrison tried valiantly to fight them. Raining cannon fire on them, the beasts suffered immense damage. However, their regeneration quickly repaired the injuries and their advance was inevitable. The garrison was the first victim of this new attack, being consumed by the beasts.

With the defense gone, the creatures breached the towns. Debris rained from destroyed structures as the nightmarish beings feasted on humans. The rampage left the outer walled area in ruins, with countless casualties. Over a span of two years, the survivors made their way into the inner walled area. They were forced to survive with less, suffering from the loss of the Yuen farm lands that were in the outer walled area.

Finding themselves in such hardships, humanity attempted to repair the outer wall. The plan was to collapse the top of the barrier to seal the hole below. Multiple parties were dispatched to achieve this. However, each was ambushed on their way by Titans, destroyed before they could achieve their goal.

Humanity did not give up, though. A new expedition, accompanied by the director of the Military Police, was formed. They were briefed on the weaknesses of the creatures, but also warned that the Titans' hearing was exceptional, tuned to the voices of humans. The group also planed to take omni-directional mobility (ODM) gear with them as well. The ODM was designed to strike the weak point of the Titans: the nape. This was done through releasing anchors into tall objects, like buildings, to allow the user to become airborne. Once at an appropriate height, the user would slash at the nape, killing the Titan. The gear took an individual with tremendous skill to achieve this.

Heading off, the group embarked for Omote City, where the last explosive stockpile was kept. As a result, if successful in retrieving them, this would be the last expedition to attempt the trip to the wall. To increase their chances of success, the plan was to move primarily at night to avoid detection. The group moved by vehicle, traveling through the destroyed outer area.

Along the way, the expedition paused, fearing something was nearby. They found the source to be some cattle, for whom the Titans had no interest in as they dieted exclusively on humans. While checking, though, two members of the group, Hiana and Eren, wandered off alone after hearing a cry. Hiana stumbled upon a baby Titan as the source of the noise, who was chewing on a human. The infant monster went on the attack, but was unsuccessful. Frustrated, the baby began to cry, attracting other Titans to the area.

The wailing caused a frenzy, as Titans rushed to the scene, with a larger one even crushing a smaller one in its haste. Amidst the chaos, the garrison captain warned against raising their voices. It was too late, however, as a Titan grabbed the captain and killed him. As more Titans appeared, the director and others leave in the vehicles, abandoning recruits. The garrison commander, Hans, shouted from a vehicle for the others to seek cover. What resulted was a bloodbath as they tried to defend themselves. This included one instance where a Titan tried to grab a soldier, only to be thrown by a small human with a shoulder toss, displaying the beast's relatively light weight.

On foot, a group of survivors reached Omote City. Their path was blocked by a Titan, although the creature was killed with a slash to its back neck with the ODM. The killer was Shikishima, captain of the Scout Regiment who survived a previous failed attempt to repair the wall. Another Titan advanced, but was similarly killed by the captain's chief, Mikasa Ackerman.

Afterwards, the survivors met up with the vehicles from the expedition. Together, they secured the explosives and setup a temporary camp in the nearby demolished buildings.

That night, while resting, the group was ambushed by the Titans. The first causality was Hiana, as a Titan grabbed and ate her before Eren's eyes. The group's commander, Hans, alerted the others to the assault. Equipping the ODMs, the troops went on the offensive. One member went around slashing the Achilles tendons on Titans, momentarily crippling them. Another soldier attempted to go for the neck, but was smashed into a wall, killed on impact. Meanwhile, Shikishima and Mikasa went on the attack. Shikishima killed two of the beasts, wrapping the legs of one before slicing the nape, while his chief similarly took down two as well.

In the meantime, Hans witnessed one of the vehicles with the explosives leaving. Realizing it was being stolen, the commander alerted others to secure it. However, a grief stricken soldier, who just lost her boyfriend, had other ideas. She ignited the explosives and kicked out the masked thief. She then drove the vehicle head on into the Titans, damaging them in a suicide run from the resulting explosion.

With moral gone, realizing the loss of the explosives, Eren watched as the Titans devoured his comrades. Rage building, he used his ODM and flew directly at the Titans. Dodging their attacks, he killed one of the Titans. In a moment of victory, he become distracted, allowing another Titan to bite off his leg in midair. He then collapsed, weakened, on top of a building.

Meanwhile, another soldier was trapped on a nearby roof. Surrounded by Titans, others attempted to save him by firing flares, distracting the beasts. As one of the creatures approached, a troop blinded it with arrows that pierced its eyes. Another slashed the Achilles tendons, while the trapped soldier used the ODM to land the killing blow. Afterwards, one of the troops was informed of Eren's misfortune. Distracted by the news, the soldier was grabbed by a Titan.

Eren saw the soldier being lifted, as another shot arrows into the Titan's arm in an unsuccessful bid to save him. Others attempted to slash the Titan's tendons and nape, but neither effort was successful. As the beast shoved the soldier in its mouth, Eren suddenly appeared and threw the soldier to safety. Unfortunately, Eren was unable to save himself, as the Titan bit down, severing Eren's arm and eating him. Inside, Eren discovered the half digested corpse of Hiana, sending him into a blinding rage.

With odds increasingly against them, Mikasa arrived to help the survivors escape. Confident, the chief told them she would carve them a path through the Titans, and leaped off using her ODM. Killing the creatures as she went, the ODM ran out of gas, causing her to fall helplessly to the ground.

The Titan that swallowed Hiana and Eren then advanced on her, but the beast started to contort in pain. Suddenly, two large hands appeared out of the creature's mouth and ripped it apart from the inside. What emerged from its corpse was a new Titan, the Attack Titan. The creature let loose a roar, drawing the other Titans to it. Immediately afterwards, the new Titan went berserk. With powerful punches, the rogue Titan smashed the heads of the others, killing them with each blow.

Afterwards, the rogue monster briefly attacked the survivors, before collapsing. The group then removed Eren from its nape, revealing its identity to be the young soldier.

Later, Eren was questioned by the Military Police at Omote City. Unsatisfied with his responses, his execution was ordered. Luckily, another Titan, an Armored Titan, arrived. Saving Eren, the two vanished.

Much later, they emerged together before the survivors, although quickly turn on one another. Eren's goal was still to save humanity, while Shikishima, the true identity of the Armored Titan, wished to take down the ruling class. Changing into his armored form, Shikishima chased the survivors to the wall. His presence, however, attracted other Titans to the area. The armored creature proved a quick victor, though, destroying the Titans with powerful punches to their heads.

Eventually, Eren transformed into his rogue form and the two did battle. The Attack Titan narrowly claimed victory, skewering his armored opponent. Eren then grabbed an ancient bomb in the area and with the survivors attempted to lodge it in the wall. Eren changed back while the director of the military police arrived. After a brief skirmish, the director was revealed to be the Colossal Titan. A tough battle ensued, eventually claiming the Colossal Titan's life in an explosion. This also sealed the hole in the wall, ending the Titan's advance through the outer wall.

Powers / Weapons

Super Regenerative Power

The large monsters could recover from severe damage. This process released steam, as their bodies heated to repair injuries at incredible rates.

There was seemingly no limit to the level of damage they could recover from. On rare occasion, their bodies would show scaring, though. Most often this scaring appeared around the mouth area, exposing more of their teeth and gums as a result.

Weaknesses

Nape

The Titans possessed a fatal weakness on the back of their neck. If pierced, the creature would be killed. Once exterminated, the body of the Titan would vaporize, leaving behind no evidence. The attack would have to pierce the right area, though. If too low, steam would be released and the Titan would be fine.

While the back of the neck was their weak point, similarly destroying their entire head would also kill them. This was the preferred tactic of both the Attack and Armored Titans.

Background and Trivia

On the official English website for the movies, "medium" Titans are listed as 23 feet tall. This is roughly 7 meters in height. However, in the movies the Titans are observed to come in varying sizes. This includes both a baby and also a smaller Titan that is stepped on by a larger one.